The present disclosure relates to an organic EL element, a display device, and an illuminating device.
In recent years, as a light emitting element driven at a lower voltage, an organic electro-luminescence (EL) element that has a light emitting layer that contains an organic compound (which will also be referred to hereinafter as an organic light emitting layer) has been noticed. In addition, various technologies relating to a display device and an illuminating device that use such organic EL elements (which will also be referred to hereinafter respectively as an organic EL display device and an organic EL illuminating device) have been developed.
In such an element, a wavelength band of light emitted from an organic light emitting layer composed of a single material is limited to a given range, and thus it is difficult to cause the organic light emitting layer composed of a single material to emit white light. Thus, an organic EL element in which a plurality of organic light emitting layers that emit light having different wavelength bands are arranged in an in-plane direction or in a stacking direction and the organic light emitting layers are caused to emit light at the same time to generate white light has been proposed. For example, JP 2003-272860A discloses a technology for realizing higher light emission efficiency of an organic EL element in which a plurality of organic light emitting layers are arranged in a stacking direction (which will also be referred to hereinafter as a stacking-type organic EL element or a tandem-type organic EL element) by adjusting a specific resistance value of an intermediate layer such as a charge generation layer inserted between the organic light emitting layers.
On the other hand, it is not easy in a stacking-type organic EL element to maintain a uniform light emission ratio of each organic light emitting layer over a wide range of light emission luminance levels. Thus, chromaticity of light emitted from a stacking-type organic EL element changes, for example, as light emission luminance changes, and thus it is difficult to stably emit uniform white light. There is a concern of occurrence of such a change in chromaticity, which leads to deterioration in image quality of a display device in which such stacking-type organic EL elements are mounted. Thus, for example, JP 2012-194256A discloses a technology with respect to a display device that has pixels constituted by sub pixels which emit light of colors including red, green, blue, and white for suppressing a change in chromaticity of light emitted from the pixels over a wide range of light emission luminance levels by adjusting luminance of each sub pixel.